The present invention relates to an electron beam recorder having incorporated therein a contrast compensating circuit capable of providing the picture signal to be supplied to an electron beam recorder with a pre-distortion whereby contrast in the picture on a film or the like is improved.
In a film recorder such as to produce a movie film from a video signal, it is a general practice that the video signal is first recorded in a VTR or the like and then subjected to editing operation and the thus edited picture signal is supplied to the film recorder while being reproduced at the speed corresponding to the processing time of the recorder.
As the stylus (pen point) for exposing the film, those using a CRT spot, laser beam, electron beam, etc. are known, of which the recorder using the electron beam (EBR) is specifically suitable for high resolution monochromatic recording. In such a recorder, as shown in FIG. 5, for example, a film 11 disposed in a vacuum device 10 from which air is exhausted is directly exposed to an electron beam 13 emitted from an electron gun 12 while the electron beam 13 is caused to scan the film by means of a deflection device 14, and thereby, a master movie flim is produced.
The electron beam 13 is made into a fine beam spot by a converging lens or the like and modulated by the picture signal S.sub.v and thereby pictures are recorded on the film 11 in one frame after another.
The density distribution of the electron beam, however, is microscopically represented by a curve having a certain degree of spread as shown in FIG. 6. Therefore, there has been a problem that, as the electric current density becomes higher, the frequency characteristic of the film is deteriorated by this spread present in the curve, and the contrast in the picture is thereby lowered.
More particularly, when a picture signal S.sub.v consisting of white and black levels formed of a high frequency component as indicated in FIG. 7(a) is supplied, the bases of the spread electron beam on account of the above described spreading overlap each other, as indicated in FIG. 7(b), in the regions of valleys t.sub.1, t.sub.2 which should originally be reproduced white, whereby exposure of the film takes place even at these portions. As the result, as indicated in FIG. 7(c), the white portions is reproduced in substantially gray color and the original contrast C.sub.r is reduced to the lower contrast C.sub.r '.
Therefore, even if a picture signal A of a wide frequency band as indicated in FIG. 8 is supplied, the frequency characteristic for the picture reproduced on the film is deteriorated as indicated by the frequency band labeled F, and as a result the resolution of the picture becomes inferior.
Accordingly, the present invention was made with the object to provide an electron beam recorder having incorporated therein a contrast compensating circuit whereby the disadvantages of conventional recorders would be reduced and a picture with high resolution would be obtained.